Patent Document 1 discloses one example of a fuel injection valve. In the fuel injection valve disclosed in Patent Document 1, fuel pressure in a control chamber acts to bias a nozzle needle in a closing direction. In this fuel injection valve, pressure in the control chamber is manipulated to control opening and closing operation of a nozzle needle.
More specifically, the fuel injection valve has a control chamber communication passage, which is communicated regularly with the control chamber. In this fuel injection valve, fuel in the control chamber is exhausted through the control chamber communication, passage and an exhaust passage into a low-pressure portion. In this way, fuel pressure in the control chamber is reduced thereby to move the nozzle needle in the opening direction. In addition, high-pressure fuel is supplied from a high-pressure passage through the control chamber communication passage into the control chamber. In this way, fuel pressure in the control chamber is increased thereby to move the nozzle needle in the closing direction.
This fuel injection valve includes a valve element accommodated in a valve chamber. The valve element controls communication between the control chamber communication passage and the exhaust passage and communication between the control chamber communication passage and the high-pressure passage. A valve element spring biases the valve element in a direction to block the control chamber communication passage from the exhaust passage. In addition, an actuator using a piezoelectric element actuates the valve element in a direction to block the control chamber communication passage from the high-pressure passage.
A closing speed of the needle may be desirably set high in order to retain an accuracy of an injection quantity. The closing speed of the needle may be set high by increasing a passage area of a throttle of the high-pressure passage.
It is noted that, the control chamber communication passage is blocked from the high-pressure passage in a needle closing state. In the needle closing state, the valve element is applied with a force caused by pressure of high-pressure fuel in a direction to communicate the control chamber communication passage with the high-pressure passage. Therefore, if the passage area of the throttle in the high-pressure passage is enlarged, an area, in which the valve element receives the pressure of high-pressure fuel, also increases in the state where the control chamber communication passage is blocked from the high-pressure passage. Consequently, the actuator is requested to produce a large actuating force to cause the valve element to retain the control chamber communication passage blocked from the high-pressure passage. That is, the actuator may be enlarged.
The fuel injection valve disclosed in Patent Document 1 utilizes, as an assist pressure, pressure in the valve chamber and the control chamber, when the valve element blocks the control chamber communication passage from the high-pressure passage, In this way, hydraulic pressure is applied onto the valve element in a direction to assist an actuating force of the actuator. Thus, the configuration of the fuel injection valve may reduce an actuating force required to the actuator.
(Patent Document 1)
Publication of unexamined Japanese patent application No. 2006-46323
It is noted that, in the fuel injection valve of Patent Document 1, hydraulic pressure acts as the assist pressure onto the valve element in the direction to assist the actuating force of the actuator when the control chamber communication passage is blocked from the high-pressure passage. To the contrary, high-pressure fuel also applies hydraulic pressure in a direction to oppose to the actuating force of the actuator.
It is further noted that, pressure of high-pressure fuel is higher than the assist pressure. Therefore, the hydraulic pressure in the direction to oppose to the actuating force of the actuator is greater than the hydraulic pressure in the direction to assist the actuating force of the actuator.
It may be assumable to increase a common rail pressure, which is pressure of high-pressure fuel, further than a pressure in the current status in order to, for example, improve a combustion state in an internal combustion engine. It may also be assumable to enlarge the passage area of the throttle in the high-pressure passage in order to increase a speed to close the needle. In those assumable cases, an actuating force required to an actuator may become greater than that of the current status. Consequently, an actuator may be inevitably enlarged.